After reading an answer at this link:
I am confused. Do ACK values repeat when a packet is lost or when an out of sequence packet is received? For example in the diagram, the ACK values are same at the 12th and 13th segment. However, there's a drastic change in the window size. What exactly is the link?
I also read that selective acknowledgments could be used in segement 8. I know what they do by definition but I don't understand why we could use them here in segment 8 particularly. Any ideas? If it's because of the same SEQ & ACK numbers in the corresponding segments, it would be the same for segment 10, right?